1. Field of the Invention
The present invention relates to ball-and-socket joints, and, more particularly, to an improved liner forming the socket of an orthopaedic implant utilized to replace (in whole, or in part) a ball-and-socket joint.
2. Description of the Related Art
Orthopaedic implants for the replacement of all, or a portion of, a patient""s joint such as, e.g., the ball-and-socket joints of, e.g., the shoulder and hip are commonly used to restore the use of, or increase the use of a joint which has deteriorated due to, e.g., aging, illness, or injury. For the sake of brevity, this document will describe a ball-and-socket joint with reference to the hip joint, however, it will be understood that the disclosure of this document is adaptable to any ball-and-socket joint, including, e.g., the shoulder joint.
Typically, orthopaedic implants for replacing a patient""s hip include a femoral component and an acetabular component. The femoral component includes the xe2x80x9cballxe2x80x9d of the joint, while the acetabular component includes the xe2x80x9csocketxe2x80x9d. The femoral component is designed to replace the head and the neck of the femur, while the acetabular component is positioned in the acetabulum and includes an articular region to receive the head of the femoral component and to allow relative movement between the femoral component and the acetabular component. The head of the femoral component is generally spherical, and the articular region of the acetabular component includes a corresponding spherical cavity to accommodate the head of the femoral component and form the desired ball-and-socket joint.
The acetabular component typically includes both a cup and a liner, with the cup being formed from, e.g., stainless steel or titanium and the liner being formed from ultra-high molecular weight polyethylene (UHMWPE). It is further known that the liner can be formed from a plastic other than UHMWPE and can also be formed from metal. The current disclosure is adaptable to the various materials of construction of the acetabular component.
In a known prosthetic hip joint, the liner of the acetabular component forms the articular region thereof. The acetabular cup is affixed to the acetabulum and the liner is thereafter affixed to the shell and receives the femoral head. Known procedures for affixation of the acetabular cup include, e.g., the use of screws to traverse apertures in the acetabular cup, be sunk into the acetabulum, and thereby effect affixation of the acetabular cup to the acetabulum. The liner of the acetabular component typically includes exterior protrusions and/or indentations which mate with indentations and/or protrusions on the interior of the shell to effect affixation of the liner to the shell and form the complete acetabular component.
The acetabular component described above includes a single articulating surface, however, it is known to provide an acetabular component which is not affixed to, but rather is movable within the natural socket of the acetabulum and therefore includes a pair of articulating surfaces (i.e., the head of the femoral component is moveable against the articular region of the acetabular component and also the acetabular component is moveable within the natural socket of the acetabulum). These devices having a pair of articulating surfaces are generally referred to as xe2x80x9cbipolarxe2x80x9d. The constrained acetabular liner of the current invention is applicable to both of the above-described types of acetabular components.
In one known prior art hip implant, the articular region of the acetabular component is hemispherical, and, therefore, the head of the femoral component is not xe2x80x9cconstrainedxe2x80x9d or held in place by the acetabular component. In such arrangements, the muscles, tendons and ligaments of the individual receiving the implant function to hold the femoral component in place within the articular region of the acetabular component. FIGS. 1 and 2 illustrate prior art acetabular liner 20 including hemispherical articular region 22. Acetabular liner 20 further includes affixing protrusions 24 to affix acetabular liner 20 to an acetabular cup to form the complete acetabular component, as described above. Since articular region 22 will not hold the head of a femoral component in place, acetabular liners of this type may result in a relatively high incidence of hip dislocation.
Alternatives to hemispherical acetabular liners include so-called xe2x80x9cconstrainedxe2x80x9d acetabular liners. Constrained acetabular liners are characterized in that the head of the femoral component is physically restrained by the acetabular liner after being positioned in abutting relationship with the articular region of the acetabular liner. Constrained acetabular liners have a spherical articular region and are generally spherically shaped themselves. The articular region of a constrained acetabular liner is formed in a cavity of the acetabular liner which is larger than a hemisphere, so that the acetabular liner surrounds more than a hemisphere of the femoral head and, therefore, constrains the femoral head from dislocation from the acetabular component.
While constrained acetabular components advantageously decrease the frequency of joint dislocation, they present assembly problems for the surgeons who implant them. Generally, the more constrained (i.e., the more material of the acetabular liner extending beyond a hemisphere) an acetabular component is, the more difficult the ball-and-socket joint is to assemble. With this in mind, many constrained ball-and-socket joints have an assembly force which necessitates assembly of the femoral head into the articular region of the acetabular component prior to implantation (i.e., not during the surgical procedure). This assembly procedure limits the versatility of these components and, specifically, limits a surgeon""s ability to choose an alternative prosthesis during a surgical procedure.
With the above problems in mind, constrained acetabular components having an assembly force which is disproportionately lower when compared to the dislocation force of the assembled prosthesis have been developed. FIGS. 3 and 4 illustrate prior art acetabular liner 30 having spaced cuts 38 extending from beveled rim 42 into articular region 32. Acetabular liner 30 further includes affixing protrusions 34 analogous to affixing protrusions 24 described above with respect to acetabular liner 20 illustrated in FIGS. 1 and 2.
Prior art acetabular liner 30 includes petals 44 formed between adjacent cuts 38. FIG. 4 illustrates insertion of femoral component 78 into acetabular liner 30. As illustrated in FIG. 4, petals 44 flex outwardly as femoral head 80 is inserted into acetabular liner 30. FIG. 4 illustrates femoral head 80 prior to being fully seated against articular region 32. As illustrated, in this transitional state, cuts 38 separate to allow petals 44 to flex outwardly, thus increasing the size of the opening in acetabular liner 30 and decreasing the required assembly force to operatively position femoral head 80 in abutting relationship with articular region 32.
Referring to FIG. 3, acetabular liner 30 includes beveled rim 42 adjacent the opening to facilitate positioning and insertion of femoral head 80. After femoral head 80 is fully seated within acetabular liner 30, locking ring 36 will be positioned generally about the exterior portion of acetabular liner 30 surrounding beveled rim 42. When operably positioned about acetabular liner 30, locking ring 36 prevents outward flexure of petals 44, thus increasing the dislocation force required to remove femoral head 80 from acetabular liner 30.
FIGS. 5 and 6 more fully illustrate prior art locking ring 36. As illustrated, locking ring 36 includes beveled annular surface 46 to facilitate placement of locking ring 36 about acetabular liner 30. As illustrated in FIG. 4, locking ring 36 is placed about femoral neck 82 prior to being operably positioned about acetabular liner 30. Locking ring 36 utilized with this prior art prosthesis may be incorrectly positioned about femoral neck 82 (i.e., with beveled annular surface 46 being positioned on the end of locking ring 36 facing femoral stem 84, as opposed to the end of locking ring 36 facing femoral head 80) since no external indicator of the beveled surface is provided. When such mis-positioning occurs, beveled annular surface 46 is ineffective in facilitating the placement of locking ring 36 about acetabular liner 30. Furthermore, acetabular liner 30 includes a locking lip (not shown) for retaining locking ring 36 in operable position about acetabular liner 30, therefore, if locking ring 36 is mis-positioned, the locking lip will be positioned adjacent beveled annular surface 46, and, consequently, locking ring 36 will be susceptible to axial displacement and may be more easily removed from acetabular liner 30. Also, locking ring 36 can be difficult to position about acetabular liner 30, as the surgeon""s hand may slip over locking ring 36 as axial force is supplied to locking ring 36.
What is needed in the art is a constrained socket, and, specifically, a constrained acetabular liner which does not include cuts extending into the articular region.
What is further needed in the art is a locking ring for use with a constrained socket, and, specifically, a constrained acetabular component, which locking ring is structured to facilitate operative positioning thereof by a surgeon.
The present invention provides an improved constrained socket for use in an orthopaedic implant for replacing a ball-and-socket joint. In one form of the current invention, the improved socket construction is embodied in an improved constrained acetabular liner. The constrained socket of the current invention includes cuts extending from the opening of the socket generally toward, but not into, the primary articular region. For the purposes of this document, the xe2x80x9cprimary articular regionxe2x80x9d or xe2x80x9cprimary articular surfacexe2x80x9d refers to the portion of the cavity in the socket of a ball-and-socket joint in the lower hemisphere of the cavity, with the lower hemisphere defined as the portion below an equatorial line residing in a plane which is substantially perpendicular to a plane containing the rim of the socket surrounding its opening. The socket further includes an annular expansion cutout, with the aforementioned cuts terminating therein. A plurality of petals are formed between adjacent cuts and are operable to flex outwardly to facilitate operable positioning of a ball within the socket.
The constrained socket of the current invention is absent cuts on the primary articular surface, but nevertheless has a relatively low assembly force. This is due in part to the annular expansion cutout which allows sufficient outward flexure of the petals to allow insertion of the ball of a prosthetic ball-and-socket joint. The ball-and-socket joint of the current invention further includes a locking ring with an interior annular beveled surface to facilitate operable positioning of same and with an exterior visual indicator to facilitate identification of the beveled end of the locking ring. The exterior visual indicator of the locking ring of the current invention comprises an annular exterior protrusion against which axial force may be supplied to facilitate positioning the locking ring and decrease the problem associated with a surgeon""s hand slipping along the locking ring.
The invention, in one form thereof, comprises an implantable prosthetic ball-and-socket joint. The ball-and-socket joint of this form of the current invention includes a ball connected to a component adapted for affixation to an articulating bone as well as a socket having a generally spherical cavity and an opening for receiving the ball. The socket of this form of the current invention is adapted for affixation to a bony structure, and the cavity includes an articular region for abutting the ball when it is operably positioned therein. The socket further includes at least one partial exterior cut extending through the exterior of the socket, but not into the cavity. The cut allows a portion of the socket near the opening of the socket to flex outwardly to allow the ball to traverse the opening and be positioned in abutting relationship with the articular region.
The invention, in another form thereof, comprises an implantable prosthetic ball-and-socket joint. The ball-and-socket joint of this form of the current invention includes a ball connected to a component adapted for affixation to an articulating bone as well as a socket having a generally spherical cavity and an opening for receiving the ball. The socket of this form of the current invention is adapted for affixation to a bony structure, and the cavity includes a primary articular region for abutting the ball when it is operably positioned therein. The socket further includes at least one cut extending generally from the opening of the socket toward, but not into, the primary articular region of the socket. The cut allows a portion of the socket near the opening to flex outwardly to allow the ball to traverse the opening of the socket and be positioned in abutting relationship with the primary articular region.
The invention, in a further form thereof, comprises an implantable prosthetic ball-and-socket joint. The ball-and-socket joint of this form of the current invention includes a ball connected to a component adapted for affixation to an articulating bone and a socket. The socket includes a generally spherical cavity as well as an opening for receiving the ball of the joint. The socket is adapted for affixation to a bony structure and the cavity includes an articular region for abutting the ball of the joint. The socket further includes an annular expansion cutout for allowing a portion of the socket near the opening of the socket to flex outwardly to allow the ball of the joint to traverse the opening in the socket and be positioned in abutting relationship with the primary articular region.
The invention, in yet another form thereof, comprises an implantable prosthetic ball-and-socket joint. The ball-and-socket joint of this form of the current invention includes a ball connected to a component adapted for affixation to an articulating bone as well as a socket having a generally spherical cavity and an opening for receiving the ball. The socket is adapted for affixation to a bony structure, with the cavity therein including a primary articular region for abutting the ball. The socket includes at least one cut extending generally from the opening toward the primary articular region to allow a portion of the socket near the opening to flex outwardly to allow the ball to traverse the opening and be positioned in abutting relationship with the primary articular region. The implantable prosthetic of this form of the current invention further includes a locking ring for surrounding the opening of the socket and preventing flexure of the portion of the socket near the opening. The locking ring includes an interior annular beveled surface located at a first end of the locking ring, and further includes an exterior annular protrusion operable to identify the first end of the locking ring.
An advantage of the present invention is the ability to provide a constrained socket for a ball-and-socket joint which facilitates placement of the ball in the socket, but which does not include cuts extending into any portion of the articular region.
Another advantage of the present invention is the ability to provide a constrained socket for a ball-and-socket joint which facilitates placement of the ball in the socket, but which does not include cuts extending into the primary articular region.
Another advantage of the present invention is the provision of a locking ring having an external identifier to facilitate proper positioning thereof.
A further advantage of the present invention is the provision of a locking ring including a radially extending member against which axial force may be supplied to facilitate operable positioning of the locking ring.